1. Field of the Invention
The present invention relates to a method and an apparatus for efficiently defining surfaces of a three-dimensional object from a three-dimensional wire-frame model as in a three-dimensional modeling system using a computer, such as computer-aided design (CAD) and computer-aided manufacturing (CAM).
2. Discussion of the Related Art
A CAD or CAM system as disclosed in JP-A-62-251965 is adapted to newly design or re-design parts or products having a certain shape, by using wire-frame models which are relatively simple in data construction. In such a CAD or CAM system, the wire-frame models are automatically processed into desired solid models. While such wire-frame models enable a human being to imagine three-dimensional objects, each wire-frame model is nothing but a group of edges (segments), namely, consists of a list of coordinate values of vertices (apices) in a three-dimensional coordinate system, and a list of the edges or segments each connecting the adjacent vertices. Therefore, suitable processing of the wire-frame models is required to erase hidden lines, to obtain volumes or weights of the objects, or to convert them into solid models. The processing includes definition of a plurality of surfaces or faces which collectively define each three-dimensional object.
For defining the surfaces of an object from a three-dimensional wire-frame model, each of the edges is checked to determine whether this edge cooperates with any other edges connected thereto to define a closed loop. Each closed loop is defined or determined as a surface of the three-dimensional object corresponding to the wire-frame models.
To effect the above determination as to whether the closed loops are defined, multiple edges connected to each edge in question are sequentially pointed for the determination. Accordingly, the computer of the system requires a considerably long processing time for defining the surfaces from the wire-frame models. This is a drawback of the conventional system.